Unfortunatley the dota 2 lore isn't really far developed at this point of time. So this and some lines of Witch doctor that sound similar are really the only ones and there are no hints on how it developed or if there is any writing of it :/

As there is no writing of the language shadow shaman uses I took the liberty of keeping the runes I put on the book in the first place. And I replaced the skull by a coin as the ones shadow shaman originally have on his belt. Thanks again Jindor for your feedback.

@ENODMI : True, I worry a bit about what it will look like once in game.